1. Technical Field
The invention relates to photovoltaic cells and methods of making photovoltaic cells, particularly to methods of manufacturing photovoltaic cells on ZnO nanorod structures, whereas all layers of the nanorod structure are preferably prepared by chemical spray pyrolysis.
2. Background Art
Photovoltaic (PV) cell is a device that converts light energy into electrical energy. Harnessing solar energy with inexpensive materials and manufacturing methods is an important challenge. Low cost deposition techniques and new designs of PV devices are needed to reduce the production costs. There has been much interest of using nanostructures in PV devices. Dye sensitized photoelectrochemical solar cell (DSSC) based on nanoporous titanium dioxide is the most known nanostructured PV device (B. O'Regan and M. Grätzel, Nature 353, 737 (1991)). Unsolved problem with DSSC is its instability, also of its solid-state modifications. Another approach is an extremely thin absorber (eta) cell which has an extra thin absorber sandwiched between two strongly interpenetrating transparent wide band gap semiconductors (K. Ernst, et al, Semicond. Sci. Technol. 18, 475 (2003)). Most frequently used n-type nanostructured window material for the eta-solar cell is porous TiO2. Alternatively, ZnO nanowires or columnar ZnO structures have been used to prepare ZnO eta-cells (C. Lévy-Clément, et al, Physica E 14, 229 (2002)). Inorganic absorber materials like CdTe (C. Lévy-Clément, et al above; R. Tena-Zaera, et al, Thin Solid Films 483, 372 (2005)), CdSe (Lévy-Clément, et al, Advanced Materials 17, 1512 (2005); R. Tena-Zaera, et al, C. R. Chimie 9, 717 (2006); R. Tena-Zaera, et al Proceedings 21st European PV Solar Energy Conf., 4-8 Sep. 2006, Dresden, Germany (2006), p.238) or In2S3 (D. Kieven et al, Applied Physics Letters 92, 153107 (2008) have been used in ZnO based cells. The conversion efficiencies of 2.3-2.5% are reached in ZnO nanowire based eta-cells (see C. R. Chimie, above; D. Kieven et al, above).
ZnO nanowire layers for photovoltaic applications have been fabricated by electrodeposition (see C. Lévy-Clément, R. Tena-Zaera above), metalorganic vapour deposition (J. B. Baxter and E. S. Aydil, Sol. Energ. Mater. Solar Cells 90, 607 (2006)), hydrothermal growth (M. Guo, P. Diao, X. Wang and S. Cai, J. Solid State Chem. 178, 3210 (2005) and solution deposition (D. Kieven et al, above).
In US patent application to Yang et al (Publication No. US 2005/0009224A1) is described a method of growing zinc oxide nanowires (aspect ratios between about 10 to about 500) on transparent conductive oxide (TCO) covered substrate, such as glass, and dye sensitized solar cells, organic-inorganic solar cells and solid state sensitized solar cells built on such nanowires. The nanowires in Yang are deposited by solution based processes, e.g., by dip coating process.
Recently we have developed a low-cost deposition method of growing zinc oxide nanorod arrays on conductive transparent electrodes by chemical spray (M. Krunks, et al, U.S. provisional application 60/671232; international patent application PCT/EE2006/000002, published as WO2006108425).